So sorry you're dealing with POTS symptoms 😔
I've had orthostatic intolerance (NMH, POTS) since 1990. For me it's part of ME/CFS which was triggered by some unknown virus.
Have you seen this recent blog post by The Disabled Ginger?
"Learning to Live Horizontally - Your Guide to All Things POTS"
https://www.disabledginger.com/p/learning-to-live-horizontally-your